Purification of 2,4-dihydroxy-benzophenone

ABSTRACT

CRUDE 2,4-DIHYDROXYBENZOPHENONE IS PURFIED BY TREATING WITH SODIUM HYDROSULFITE IN AQUEOUS ALKALINE MEDIUM AT A PH OF AT LEAST ABOUT 7.5 AND AT A TEMPERATURE OF ABOUT 70-100*C, PRECIPITATING, FILTERING, WASHING AND DRYING.

United States Patent O 3,830,845 PURIFICATION OF 2,4-DIHYDROXY-BENZOPHENONE Fred S. Arimoto, Newark, Del., and Luke D. Ford,Pennsville, N.J., assignors to E. I. du Pont de Nemours and Company,Wilmington, Del. No Drawing. Continuation-impart of abandonedapplication Ser. No. 702,208, Feb. 1, 1968. This application Oct. 30,1970, Ser. No. 85,819

Int. Cl. C07c 49/82 U.S. Cl. 260-591 5 Claims ABSTRACT OF THE DISCLOSURECrude 2,4-dihydroxybenzophenone is purified by treat ing with sodiumhydrosulfite in aqueous alkaline medium at a pH of at least about 7.5and at a temperature of about 70-100 C., precipitating, filtering,washing and drying.

BACKGROUND This is a continuation-in-part of application Ser. No.702,208, filed Feb. 1, 1968 and now abandoned.

2,4-Dihydroxybenzophenone is a well-known ultraviolet light absorber andis also used as an intermediate in the preparation of other ultravioletlight absorbers (see U.S. Pat. No. 3,006,959). It is used extensively tostabilize colorless or lightly colored resinous, polymeric and plasticarticles, fibers, films and coatings. It is therefore of utmostimportance that the 2,4-dihydroxybenzophenone itself be of the highestpurity and stability so that it does not darken or discolor thematerials it is designed to protect.

In some processes of manufacture, such as those utilizing resorcinolwith benzonitrile (French Pat. No. 1,504,132), benzoyl chloride (U.S.Pat. No. 2,773,903) or benzotrichloride as starting materials, the crude2,4- dihydroxybenzophenone obtained is found to contain small amounts oforange-red impurities. These orangered impurities were identified as6-hydroxy-9-phenyl-3H- xanthen-3-one by Doebner in Annalen 217, page234, in the reaction of 1 mole of benzotrichloride with 2 moles ofresorcinol at 180 C.-190 C. Cohn in J. fur Praktiche Chem. [2] 48, page387, shows that the same 6-hydroxy- 9-phenyl-3H-xanthen-3-one is formedwhen one part of benzoic acid and two parts of resorcinol and one-halfpart of zinc chloride are heated at 170 C.180 C. In addition,Kornarowski and V. Kostanecki in Berichte 27, page 1998, show that thesame 6-hydroxy-9-phenyl-3H- xauthen-3-one is formed whendihydroxybenzophenone is heated with resorcinol in the presence of zincchloride indicating thereby that in reactions to producedihydroxybenzophenone the dihydroxybenzophenone produced reacts with theresorcinol to produce the orange-red impurities. Although these darkcolored materials generally do not amount to more than a few percent,they are nevertheless present in sutficient quantity to causeundesirable color formation.

Known methods of purification, such as recrystallization from solventsas described in U.S. Pat. No. 2,682,559 and U.S. Pat. No. 2,854,485, donot satisfactorily remove the colored impurities from the crude2,4-dihydroxybenzophenone. Simple recrystallization from solvents is notsufiicient to produce a dihydroxybenzophenone pure enough for use inclear plastics and coatings.

It is accordingly among the objects of this invention to provide aprocess for the purification of 2,4dihydroxybenzophenone. A furtherobject is to produce 2,4-dihydroxybenzophenone substantially free oforange-red colored impurities. Other objects will appear hereinafter.

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Patented Aug. 20, 1974 Removal of orange red impurities from crude2,4-dihydroxybenzophenone formed by the reaction of resorcinol withbenzoyl chloride, benzonitrile or benzotrichloride is accomplishedaccording to the present invention by treating said crude2,4-dihydroxybenzophenone with at least about 0.05 parts by weight ofsodium hydrosulfite per part of crude in an aqueous alkaline mediumhaving a pH of at least about 7.5 at a temperature in the range of about70-100 C. for at least about 10 minutes, isolating (precipitating) theproduct preferably by cooling or precipitating by neutralization to a pHof 4.0 or less, filtering, washing and drying. The precipitate may befurther purified by, before drying, dissolving it in acetone, addingactivated carbon, optionally heating, filtering, drowning the filtratein water to reprecipitate, filtering, washing and drying.

An alternative embodiment includes also adding a metal sequesteringagent (ethylenediamine tetraacetic acid tetrasodium salt alone or inadmixture with the sodium salt of N,N-di(2-hydroxyethyl) glycine) to thehot aqueous alkaline solution. In this embodiment, it is preferable towash the precipitate with both a water-wash and with a dilute aqueoussolution of a lower aliphatic polybasic carboxylic acid before drying.

DETAILED DESCRIPTION OF INVENTION It has now been found that thedark-colored, orangered impurities found in crude2,4-dihydroxybenzophenone prepared from resorcinol and benzonitrile,benzoyl chloride or benzotrichloride, can be substantially removed fromthe crude product by first dissolving in an aqueous alkaline solutionhaving a pH of at least 7.5, preferably 8.5-9.0. The alkaline solutionmay be prepared from sodium hydroxide, sodium carbonate or sodiumbicarbonate. About 2 to 25 parts of aqueous alkaline solution per partof 2,4-dihydroxybenzophenone is adequate, the strength being sufficientto provide a pH of at least 7.5. The solution is heated to at leastabout 70 C., preferably -100 C., and sodium hydrosulfite is added to thesolution. While the amount needed will vary with the degree of impurity,about 0.05 to 0.50 part of sodium hydrosulfite per part of crudedihydroxybenzophenone is generally sufficient. The reaction mixture ismaintained at 70-100 C., preferably at l00 C., for about 10-120 minutes(preferably 10-60'minutes) with agitation. The mixture may optionally becarried out under a nitrogen gas atmosphere to minimize oxidation. Thepurified dihydroxybenzophenone is precipitated by neutralizing to a pHof about 4.0 or less or, preferably, by gradual cooling to about roomtemperature. The precipitate is then washed with water and dried. Thepurified product so obtained may be used as an intermediate in thepreparation of various benzophenone derivatives, such as ethers (U.S.Pat. No. 3,006,959).

In the purification process of the invention, sodium hydrosulfitereduces the colored impurity to a colorless form. When the purifieddihydroxybenzophenone is precipitated by acidification of the reactionmixture, a reduced, colorless form of the impurity is precipitatedtherewith. Although the dihydroxybenzophenone recovered from theacidified solution is lighter in color, it will darken upon storage orexposure to air, due to the presence of the impurity which will oxidizeback to the original colored orm.

However, for certain uses, dihydroxybenzophenone recovered in thismanner is satisfactory, as, for instance, for use in the preparation ofethers, which are also ultraviolet light absorbers. (U.S. Pat. No.3,006,959.) These ethers are prepared by the condensation ofdihydroxybenzophenone with an alkyl bromide in alkaline medium.

Since the reduced, colorless impurity is soluble in alkali, it isremoved from the product in the washing step.

According to the preferred procedure of the invention,dihydroxybenzophenone is precipitated from the reaction mixture bycooling the mixture. The reduced form of the impurity remains in thealkaline mother liquor and pure dihydroxybenzophenone is therebyrecovered.

If the 2,4-dihydroxybenzophenone itself is to be used as a UV screener,it is preferable to give it a further treatment which comprisesdissolving the above precipitate (before drying) in acetone, addingactivated carbon (and optionally heating), filtering, washing the carbonwith acetone, drowning the filtrate in water to reprecipitate the2,4-dihydroxybenzophenone, filtering, washing with water and drying.

In the event metallic substances are present or metal equipment is usedin plant manufacture of the 2,4-dihydroxybenzophenone, it is desirableto add a metal sequestering agent as well as sodium hydrosulfite to thehot aqueous alkaline solution to remove traces of metals which may havebeen acquired during the manufacturing process. The commonly used metalsequestering agents, such as Versene (ethylenediamine tetraacetic acidtetrasodium salt) and Versene Fe-3 (a mixture of ethylenediaminetetraacetic acid tetrasodium salt and the sodium salt ofN,N-di(2-hydroxyethyl) glycine), are convenient. About 0.01 to 0.02 partby weight of the metal sequestering agent per part of crudehydroxybenzophenone is generally sufiicient. More may be employed ifgreater metal contamination is present. In this embodiment, afterprecipitation, filtering and water-washing, it is preferable to wash theproduct with a dilute (in the order of about 0.1 to 0.5% beingsutficient) aqueous solution of a lower aliphatic polybasic carboxylicacid such as citric or oxalic acid before drying.

EXAMPLES The following examples describe the invention in furtherdetail. These examples are intended to be merely illustrative of theinvention and not in limitation thereof. All parts are by weight unlessotherwise indicated.

The purity (i.e., removal of the orange-red impurities) is expressed inpercent transmittance of a solution by weight in acetone as measured ina Bausch and Lomb Spectronic Colorimeter at 475 In, in optically matchedtest tubes having a one-half inch internal diameter. A higher degree oftransmittance indicates greater purity. The degree of purity desireddepends on the intended end use.

EXAMPLE 1 To a sample of 10 parts of crude orange-colored 2,4-dihydroxybenzophenone (prepared from resorcinol and benzonitrile) and 60parts of water was added 10.6 parts of aqueous NaOH (sodium hydroxide).The mixture was heated to 87 C. Five parts of sodium hydrosulfite wasadded to the solution and the latter was maintained at 87 C. for anadditional 25 minutes. The mixture was then acidified to a pH of 1.7with 9.4 parts of concentrated I-ICl and cooled to C. The light-yellowproduct (9.3 parts) melted at 144-145 C. and had a 57% transmittance.

EXAMPLE 2 The purified product obtained in Example 1 was given furthertreatment by dissolving in acetone, adding a small amount of activatedcarbon, boiling a few minutes and cooling. The carbon was removed byfiltration and the filtrate poured into water, precipitating the furtherpurified, 2,4-dihydroxybenzophenone (hereinafter designated DHBP) as afaintly yellow to white product.

EXAMPLE 3 A mixture of 41.8 parts of an aqueous 5% Na CO solution, 10parts crude DHBP (517% transmittance) and 1 part sodium hydrosulfite washeated to 95 C. and maintained at 95 C. for 10 minutes. To this mixturewas added 2 parts activated carbon (Darco) and the mixture was filteredat -100 C. The filtrate was cooled to 25 C., the precipitate filtered,washed and dried. The purified DHBP (3 parts) had a transmittance of79%. Thus, where DHBP itself is to be used as a UV screener, it ispossible if desired to combine the hydrosulfite treatment and theactivated carbon purifying treatment.

EXAMPLE 4 228 parts water and 12 parts Na CO were charged into an enamelkettle. At 80 C., parts crude DHBP (5- 17% transmittance) was added,slowly heated to 94 C. and maintained at 94 C. for 15 minutes. 12 partssodium hydrosulfite was added slowly over a 30minute period, held at 94C. for 15 minutes and cooled to about 35 C. The precipitated DHBP wasfiltered on a suction filter and washed with water. This procedure wasrepeated with another 120 parts of crude DHBP. The total solids werethen dissolved in 192 parts of acetone, decolorized with 10 partsactivated carbon (Darco 6-60) and filtered. The acetone filtrate wasdrowned in 960 parts water, the precipitated product collected on anutsch filter and then dried in a vacuum over at 60 70 C. The purifiedDHBP had a melting point of -l46 C. and a transmittance of 79%. After 24hours in a 100 C. oven, the transmittance was still about 79%. The UVspectra (ethanol) was identical to authentic DHBP.

EXAMPLE 5 A mixture of 100 parts crude DHBP (having a transmittance of25%), parts distilled water and 8 parts sodium carbonate was heated to9698 C. to give a clear solution. Ten parts of sodium hydrosulfite wasadded and the mixture was held on temperature for 10 minutes. Themixture was cooled to 25 30 C., filtered and the precipitate was washedwith distilled water until free of alkali when tested on BrilliantYellow paper. Some of the cake (79.6 parts total) was dried at 60 C. andthe dried product had a transmittance of 72% while the rest of the cakehad a transmittance of 64% after being dried at 100 C.

EXAMPLE 6 A mixture of 50 parts crude DHBP (transmittance of 25%), 95parts distilled water, and 4 parts sodium carbonate was heated to 9698C. Then 5 parts sodium hydrosulfite was added and the mixture was heldon tem perature for 10 minutes. The mixture was cooled to 25 30 C. tocrystallize the product which was then filtered and washed withdistilled water until free of alkali when tested on Brilliant Yellowpaper. The filter cake was dissolved in 51.4 parts acetone, and 0.05parts activated carbon (Darco G-60) and 0.25 parts diatomaceous earth(Standard Super Cel) were added. After stirring for 10 minutes, themixture was filtered and the cake was washed with 5.1 parts acetone. Thefiltrate was drowned into 208 parts distilled water to precipitate theproduct which was then filtered and washed with 100 parts distilledwater. Some of the product (37.9 parts total) was dried at 60 C. and hada transmittance of 93% and the remainder was dried at 100 C. and had atransmittance of 89%.

EXAMPLE 7 A mixture of 50 parts crude DHBP (transmittance of 25%), 95parts distilled water and 4 parts sodium carbonate was heated to 9698 C.over 2 hours to dissolve the DHBP. Then 0.5 part ethylenediaminetetraacetic acid tetrasodium salt and 5 parts sodium hydrosulfite wereadded, the mixture stirred for 10 minutes and then cooled to 2530 C.over 2 hours. The mixture was filtered and washed with distilled wateruntil the filtrate no longer gave an alkaline test on Brilliant Yellowpaper. The cake was washed with 100 parts of a 0.2% solution of oxalicacid in water and dried at 60 C. in a vacuum oven in a nitrogenatmosphere. A purified product, 40.3 parts (81% recovery), was obtainedhaving a transmittance of 99%. The thermal stability of the purifiedproduct was good as shown by the fact that a sample heated at 100 C. for16 hours had a transmittance of 97%.

In the above experiment, when 100 parts of a 0.1% solution of oxalicacid in water was used in place of the 0.2% oxalic acid solution, thesample when heated at 100 C. had a transmittance of 91%. If the oxalicacid wash was omitted, the sample heated at 100 C. had a transmittanceof 86%. If the ethylenediamine tetraacetic acid tetrasodium salt wasomitted and the product washed with 100 parts 0.1% oxalic acid solution,the sample heated at 100 C. had a transmittance of 85%.

EXAMPLE 8 A mixture of 150 parts crude DI-IBP (having a transmittance of25%), 285 parts distilled water, 12 parts sodium carbonate and 1.5 partsVersene Fe N0. 3 was heated to 9698 C. to give a clear solution. Then 15parts sodium hydrosulfite was added and the mixture was held at 96-98 C.for minutes. The mixture was cooled to 2530 C., filtered and washed withdistilled water until the filtrate was alkali free when tested onBrilliant Yellow paper. The cake was divided into 3 parts. The firstthird was dried, the second third was washed with 100 parts of a 0.2%solution of oxalic acid in water and dried, and the third part waswashed with 100 parts of a 0.2% solution of citric acid in water anddried. The following table gives the transmittance of the dried samples.

Optical transmittance after drying at- First third 89 85 Second third 9390 Third third 92 89 What is claimed is:

1. A process for the removal of orange-red impurities from crude2,4-dihydroxybenzophenone formed by reacting resorcinol with a compoundselected from the group consisting of benzoyl chloride, benzonitrile andbenzotrichloride which comprises dissolving said crude2,4-dihydroxybenzophenone in an aqueous alkaline solution havmg a pH ofat least about 7.5, heating said solution to at least about C., addingto said solution at least about 0.05 part by weight of sodiumhydrosulfite per part of said crude, maintaining said solution at fromabout 70 to C. for at least about 10 minutes, precipitating said2,4-dihydroxybenzophenone by cooling to about room temperature andrecovering the purified 2,4-dihydroxybenzophenone by filtering, washingand drying.

2. Claim 1 further comprising, before drying, dissolving saidprecipitate in acetone, heating in the presence of activated carbon,filtering, reprecipitating said 2,4-dihydroxybenzophenone by drowning inwater, filtering and washing.

3. Claim 1 further comprising adding to said hot aqueous alkalinesolution at least about 0.01 part by weight per part of said2,4-dihydroxybenzophenone of a metal sequestering agent selected fromthe group consisting of ethylenediamine tetraacetic acid tetrasodiumsalt and a mixture of ethylenediamine tetraacetic acid tetrasodium saltand the sodium salt of N,N-di(2-hydroxyethyl) glycine.

4. Claim 3 wherein said washing step consists of waterwashing followedby washing with dilute aqueous solution of a lower aliphatic polybasiccarboxylic acid.

5. Claim 4 wherein said acid is oxalic acid.

References Cited UNITED STATES PATENTS 3,403,183 9/ 1968 Dobratz et al.260-591 2,682,559 6/1954 Stanley et al 260-591 2,921,962 1/1960 Stanley260--59l 3,387,035 6/1968 Gray et a1. 260-591 2,854,485 9/1958 Stanley260591 FOREIGN PATENTS 278,325 1928 Great Britain 260-591 OTHERREFERENCES Van Allen et al.: J. Org. Chem, vol. 19 1954 pp. 1243 w 1251.

JOSEPH E. EVANS, Primary Examiner

